cjs-202409-0003 ArticleInAPeriodical 2024 Czech Journal of Animal Science 69 9 356-366 WangHanSzu LiaoHanHsiao Chia-XinLee ChenHsiao-Ming ChenLing-You ChuangShih-Te HsuJih-Tay The effect of different forages on rumen microbiota and milk production performance in Holstein dairy cows Optimising the feed composition, especially the forage choice, and reducing costs are essential for improving dairy production efficiency. Different forage sources and proportions were used to formulate rations containing equal energy and protein, and their effects on rumen microbiota and milk production performance of dairy cows were evaluated in two experiments. In experiment 1, thirty lactating cows (235 ±13 d postpartum; milk production 29.1 ± 1.0 kg/day) were divided into Pangola and Bermuda groups. In experiment 2, twenty lactating cows (79.9 ± 8.1 d postpartum; milk production 34.7 ± 0.6 kg/day) were divided into Pangola and oat groups. In experiment 1, the Simpson index for rumen microbiota of the Pangola group was significantly higher than in the Bermuda group (P < 0.05). Analysis of the weighted unique fraction (UniFrac) distances indicated significant differences in the beta diversity of the community composition of rumen microbiota between Pangola, Bermuda and oat groups in both experiments (P < 0.001). The relative abundance of Prevotella brevis was significantly higher in the Pangola group than in the oat group in experiment 2 (P < 0.05). The somatic cell counts (SCCs), C18:0, and C18:1 in milk were significantly higher in the Bermuda group than in the Pangola group (P < 0.05) in experiment 1. On the other hand, milk crude protein (CP) and solids-not-fat (SNF) were significantly higher in the Oat group than in the Pangola group (P < 0.05) in experiment 2; however, milk urea nitrogen (MUN) was significantly higher in the Pangola group (P < 0.05). In conclusion, a switch of forage (Pangola vs Bermuda) at a lower proportion of the diet under the high forage level condition (experiment 1) caused only minor changes in rumen microbiota diversity (Simpson index, beta diversity) and milk production performance (milk SCCs, C18:0 and C18:1). On the other hand, a switch of forage (Pangola vs oat) at a higher proportion of the diet under the low forage level condition (experiment 2) resulted in greater changes in rumen microbiota diversity (beta diversity, relative abundances of bacterial taxa, P. brevis relative abundance) and milk production performance (milk CP, SNF, and MUN).